Soil salt and groundwater change in flood irrigation field and uncultivated land: a case study based on 4-year field observations

Salt transport in soil profile and shallow groundwater changes are significant seasonal response to flood irrigation in arid area. Understanding soil salt and groundwater level change is useful to determine irrigation schedule and agricultural development. In this study, based on observation data at six fixed sites from 2007 to 2010, soil salt and groundwater depths change were investigated in irrigation fields and uncultivated lands of upper, middle and lower reaches in the arid irrigation district of Hetao irrigation district. The results indicated that the fluctuation of soil salinity in each layer in irrigation fields was more frequent, while the soil salinity in uncultivated lands presented a surface accumulation phenomenon. The groundwater level had similar trends in 4 years and the groundwater changed gradually deeper from upstream to downstream. Meanwhile, relationships between soil surface salinity and groundwater depth were various for irrigation field and uncultivated land. Furthermore, the groundwater recharge and evapotranspiration were calculated with water table fluctuation method. In all the crop growth periods, the influence of groundwater recharge on evapotranspiration was significant. For the irrigation fields, the mean contributions of groundwater to evapotranspiration of 4 years in upper, middle and lower reaches were 25.57, 11.96 and 15.23 %, respectively, while the values were 53.92, 21.61 and 36.84 % at the uncultivated land, respectively. The results can contribute to determine the water resources management plan for sustainable development of the irrigation district with shallow groundwater.